This invention relates in general to scrap metal salvage and, more particularly, to the recovery of metal which has been encased in a coating of polyvinyl chloride.
Heretofore, various procedures have been attempted to recover metals, such as copper, from insulation, as well as from a multiplicity of conditions of use wherein the same have been covered by nonmetallic organic coatings. Such efforts have been relatively complex and costly as exemplified by the disclosure of U.S. Pat. No. 2,815,278 which teaches the charging of organically coated metal to a furnace for effecting destructive distillation of the coating and involving melting of the metal to be recovered. More recently, polyvinyl chlorides have come into widespread use as insulation material of choice, but the removal of the same has proved consistently difficult so that recovery of metals, such as, copper insulated with such material, has been of but limited extent, thereby causing a substantial economic loss. Techniques for removing polyvinyl chloride coatings have been of various types; one of which is mechanical in nature, wherein the scrap is subjected to chopping by suitable instrumentality.
Another method is taught by U.S. Pat. No. 4,189,329 wherein the metal having a halogen-containing plastic coating is immersed within a heated fluidized bed containing a reactive carbonate composition for effecting thermal decomposition of the coating. The bath is heated to and maintained at the appropriate temperature for effecting such thermal decomposition, but being below calcination temperature. In this connection U.S. Pat. No. 3,480,477 also discloses a method for removing electrolytic grade copper from copper wire which has been insulated primarily by polyvinyl chloride, wherein the wire is chopped and sieved into small pieces and then placed in a sealed autoclave with circulation of petroleum distillate oil therethrough having certain prescribed ingredients, and at a temperature of at least 450.degree. F.
The Schub U.S. Pat. No. 2,435,239 discloses a process for removing a polyvinyl formal resin coating which involves treating the resin with a concentrated aqueous solution of formic acid for penetrating the resin and effecting a softening and swelling thereof to conduce to mechanical removal.
U.S. Pat. No. 2,417,468 reveals a process for removing a plastic coating from metal, such as copper wire, which comprehends subjecting the coated wire to a hot bath as in the neighborhood of 400.degree.-500.degree. F. of fatty acids of at least 16 carbon atoms for causing swelling of the coating and breaking the bond thereof. A second heated bath is then used of a predetermined solvent for dissolving the softening agent and rendering the coating readily strippable.
In view of the foregoing, it will be seen that among the expedients heretofore utilized has been mechanical removal without prior treatment; subjection of the plastic clad wire to various heated baths for swelling and loosening of the coating to make it more readily removable; as well as decomposition of the coating through suitable reagents under prescribed conditions, all of which have recognized drawbacks in view of the complexity of the last two mentioned types of procedures and the time consuming, difficult method of removal through mechanical means in view of the bond between the copper and the coating.
It must be further recognized that with polyvinyl chloride there is implicit a pollution hazard since burning of the same in the atmosphere causes the released chlorine, either as a gas or as hydrogen chloride, to be charged to the ambience wherein hydrochloric acid is developed by reason of atmospheric moisture content. This acid is deleterious to many materials incorporated in neighboring constructions, as well as being unpleasant for individuals.
Therefore, it has been found that a procedure chemically in character which does not involve burning, but which may be effected under atmospheric conditions, thereby obviating the need for carefully controlled reagent baths with the attendant use of costly equipment and the elimination of the need for laborious mechanical stripping, has been indicated. The present invention thus contemplates the simple step of subjecting the polyvinyl chloride clad metal, such as copper wire, to a bath of tetrahydrofuran, sometimes called furfuran, under ambient conditions bringing about a removal of the resin coating without release of any polluting ingredients to the atmosphere and without requiring any mechanical stripping steps.
Therefore, it is an object of the present invention to provide a method for recovering of metal, primarily copper, from a coating of organic material, such as, particularly, polyvinyl chlorine, in a one step procedure which obviates release of chloride to the atmosphere and which does not require physical stripping of the coating.
Another object of the present invention is to provide a method of the character stated which is performed with facility, requiring very simply constructed, easily operated, and highly durable equipment, and without necessitating any particularly developed skills on the part of the operator.
It is a further object of the present invention to provide a method for recovering metal, exemplary of which is copper wire, normally encased within polyvinyl chloride which may be accomplished in minimum time and at marked economies over procedures heretofore adopted and practiced, all of the same being brought about without pollution.
It is a still further object of the present invention to provide a method for recovering metal, such as copper, from polyvinyl chloride coatings which does not alter in any way, or adversely affect, the metal salvaged so that the same is capable of further processing, if desired, in accordance with current techniques.